Multilayer Waveplate Optical Structures

ABSTRACT

An optical structure includes an input grating and a multilayer waveplate. The input grating is configured to incouple a first spectrum of received image light. The multilayer waveplate is configured to reflect the first spectrum of the image light incoupled by the input grating in the second polarization orientation and reflect a second spectrum of the image light incoupled by the input grating by diffraction in the first polarization orientation.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. non-provisional applicationSer. No. 15/926,918 filed Mar. 20, 2018, which is hereby incorporated byreference.

TECHNICAL FIELD

This disclosure relates generally to optics, and in particular tooptical structures for directing image light

BACKGROUND INFORMATION

Head Mounted Displays (HMDs) are commercially available to facilitateaugmented reality (AR) and/or Virtual Reality (VR) experiences forwearers of the HMDs. In AR and VR experiences, the HMD delivers imagesto an eye or eyes of the wearer. Delivering high quality images to usersof the HMD is desirable, although space and/or weight constraintsinherent to HMDs may present design challenges for delivering highquality images to the user. Other design contexts also place a highvalue on delivering high quality images within certain designconstraints.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting and non-exhaustive embodiments of the invention aredescribed with reference to the following figures, wherein likereference numerals refer to like parts throughout the various viewsunless otherwise specified.

FIG. 1 illustrates an example Head Mounted Display that includes atleast one waveguide for directing image light to an eyebox area, inaccordance with an embodiment of the disclosure.

FIG. 2 illustrates a red, green, and blue stacked waveguide.

FIG. 3 illustrates example waveguides that include a multilayerwaveplate, in accordance with an embodiment of the disclosure.

FIG. 4 illustrates example configurations of the multilayer waveplatesillustrated in FIG. 3, in accordance with an embodiment of thedisclosure.

FIG. 5 illustrates example waveguides that include a multilayerwaveplate, in accordance with an embodiment of the disclosure.

FIG. 6 illustrates example configurations of the multilayer waveplatesillustrated in FIG. 5, in accordance with an embodiment of thedisclosure.

DETAILED DESCRIPTION

Embodiments of waveguides that include a multilayer waveplate aredescribed herein. In the following description, numerous specificdetails are set forth to provide a thorough understanding of theembodiments. One skilled in the relevant art will recognize, however,that the techniques described herein can be practiced without one ormore of the specific details, or with other methods, components,materials, etc. In other instances, well-known structures, materials, oroperations are not shown or described in detail to avoid obscuringcertain aspects.

Reference throughout this specification to “one embodiment” or “anembodiment” means that a particular feature, structure, orcharacteristic described in connection with the embodiment is includedin at least one embodiment of the present invention. Thus, theappearances of the phrases “in one embodiment” or “in an embodiment” invarious places throughout this specification are not necessarily allreferring to the same embodiment. Furthermore, the particular features,structures, or characteristics may be combined in any suitable manner inone or more embodiments.

Throughout this specification, several terms of art are used. Theseterms are to take on their ordinary meaning in the art from which theycome, unless specifically defined herein or the context of their usewould clearly suggest otherwise.

The optical structures that are described in this disclosure includewaveguides for directing image light to an eye of a wearer of a HeadMounted Display (HMD), among other contexts that the disclosed opticalstructures could be used in. An HMD may include a display for directingimage light to a wearer of an HMD. Viewing optics may also be includedin an HMD to route and focus the image light for the eye of thewearer/user. In some implementations, a waveguide is used to direct theimage light to the eye. However, prior implementations of waveguideshave generated undesirable ghost images, in certain contexts. The ghostimages may become more prevalent when the waveguide is not perfectlyflat (e.g. wedge shaped). In one particular context, visible light fromat least a portion of one spectrum (e.g. green light) bleeds into awaveguide that is designed to direct a different spectrum (e.g. bluelight) to the eye, which generates green ghost images.

In embodiments of this disclosure, one or more waveguides include amultilayer waveplate so that light from an unwanted spectrum that bleedsinto a particular waveguide may be outcoupled from the waveguide toreduce ghost images that are presented to the eye. These and otherembodiments are described in detail below.

FIG. 1 illustrates an example Head Mounted Display (HMD) 100 thatincludes at least one waveguide for directing image light to an eyeboxarea, in accordance with an embodiment of the disclosure. HMD 100includes frame 114 coupled to arms 111A and 111B. Lenses 121A and 121Bare mounted to frame 114. Lenses 121 may be prescription lenses matchedto a particular wearer of HMD or non-prescription lenses. Theillustrated HMD 100 is configured to be worn on or about a head of auser of the HMD.

In FIG. 1, each lens 121 includes a waveguide 150 to direct image lightgenerated by a display 130 to an eyebox area for viewing by a wearer ofHMD 100. Display 130 may include an LCD, an organic light emitting diode(OLED) display, micro-LED display, quantum dot display, pico-projector,or liquid crystal on silicon (LCOS) display for directing image light toa wearer of HMD 100.

The frame 114 and arms 111 of the HMD may include supporting hardware ofHMD 100. HMD 100 may include any of processing logic, wired and/orwireless data interface for sending and receiving data, graphicprocessors, and one or more memories for storing data andcomputer-executable instructions. In one embodiment, HMD 100 may beconfigured to receive wired power. In one embodiment, HMD 100 isconfigured to be powered by one or more batteries. In one embodiment,HMD 100 may be configured to receive wired data including video data viaa wired communication channel. In one embodiment, HMD 100 is configuredto receive wireless data including video data via a wirelesscommunication channel.

Lenses 121 may appear transparent to a user to facilitate augmentedreality or mixed reality where a user can view scene light from theenvironment around her while also receiving image light directed to hereye(s) by waveguide(s) 150. In some embodiments, image light is onlydirected into one eye of the wearer of HMD 100. In an embodiment, bothdisplays 130A and 130B are included to direct image light intowaveguides 150A and 150B, respectively.

FIG. 2 illustrates a red, green, and blue (RGB) stacked waveguide 200that could be used as waveguide(s) 150. FIG. 2 shows that RGB stackedwaveguide 200 includes a blue waveguide 210, a green waveguide 220, anda red waveguide 230. RGB stacked waveguide 200 receives image light 203.Image light 203 may be generated by a display 130, for example. Bluewaveguide 210 is configured to incouple the blue image light from imagelight 203 and direct the blue image light in an eyebox direction to aneyebox area 299. Green waveguide 220 is configured to incouple the greenimage light from image light 203 and direct the green image light in aneyebox direction to an eyebox area 299. Similarly, red waveguide 230 isconfigured to incouple the red image light from image light 203 anddirect the red image light in an eyebox direction to an eyebox area 299.

Blue waveguide 210 includes an input grating 213 configured to incouplethe blue image light and an output grating 215 is configured to directthe blue image light propagating in waveguide 210 to the eyebox area299. Waveguide 210 may rely on the Total Internal Reflection (TIR) toconfine the blue image light to the blue waveguide 210 until outputgrating 215 directs the blue image light to the eyebox area 299.

Green waveguide 220 includes an input grating 223 configured to incouplethe green image light and an output grating 225 is configured to directthe green image light propagating in waveguide 220 to the eyebox area299. Waveguide 220 may rely on the Total Internal Reflection (TIR) toconfine the green image light to the green waveguide 220 until outputgrating 225 directs the green image light to the eyebox area 299.

Red waveguide 230 includes an input grating 233 configured to incouplethe red image light and an output grating 235 is configured to directthe red image light propagating in waveguide 230 to the eyebox area 299.Waveguide 230 may rely on the Total Internal Reflection (TIR) to confinethe red image light to the red waveguide 230 until output grating 235directs the red image light to the eyebox area 299.

In FIG. 2, the blue image light is illustrated by a dashed line, thegreen image light is illustrated by a solid line, and the red imagelight is illustrated by a dash-dash-dot line. As image light 203encounters input grating 213 of blue waveguide 210, blue image light isdirected into waveguide 210 along an example optical path 271. Greenimage light passes through waveguide 210 along optical path 273 and isincoupled to waveguide 220 by input grating 223. Red image light passesthrough waveguide 210 along optical path 274 and also passes throughwaveguide 220 until it encounters input grating 233 which incouples thered image light into waveguide 230.

Notably, FIG. 2 also illustrates that some amount of green image lightbleeds into waveguide 210 along example optical path 272. The greenimage light propagates through waveguide 210 until encountering outputgrating 215 which outcouples portions of the green image light alongoptical paths 282A and 282B. However, this green image light outcoupledby the blue output grating 215 contributes to green ghost images thatare directed in the eyebox area 299. While only the green image lightoptical paths that bleed into the blue waveguide 210 are illustrated inFIG. 2, similar optical crosstalk issues may exist in the greenwaveguide 220 and red waveguide 230 that cause ghost images fromunwanted image light bleeding into the waveguides.

FIG. 3 illustrates example waveguides that include a multilayerwaveplate, in accordance with an embodiment of the disclosure. Theillustrated waveguides 310, 320, and 330, may be included in a stackedwaveguide 300, as illustrated. Stacked waveguide 300 includes an inputportion 393 and an output portion 394. The waveguides illustrated inFIG. 3 include a multilayer waveplate that acts to reduce opticalcrosstalk by outcoupling unwanted image light from the waveguides beforethe unwanted image light is directed to the eyebox area 399 by a givenoutput grating (e.g. 315, 325, or 335). Reducing the optical crosstalkmay decrease ghost images that are presented.

FIG. 3 includes a first waveguide 310, a second waveguide 320, and athird waveguide 330. First waveguide 310 is configured to incouple afirst spectrum of image light 303 into the waveguide 310 and direct thefirst spectrum into the eyebox area 399. In one embodiment, the firstspectrum of image light is blue light. The blue light may be within arange of between 450 and 480 nm, in some embodiments. Second waveguide320 is configured to incouple a second spectrum of image light 303 intothe waveguide 320 and direct the second spectrum into the eyebox area399. In one embodiment, the second spectrum of image light is greenlight. The green image light may be within a range of between 500 and550 nm, in some embodiments. Third waveguide 330 is configured toincouple a third spectrum of image light 303 into the waveguide 330 anddirect the third spectrum into the eyebox area 399. In one embodiment,the third spectrum of image light is red light. The red image light maybe within a range of between 620 and 650 nm, in some embodiments.Although the waveguides 310, 320, and 330 may be described with respectto red, green, and blue image light, it is understood by those skilledin the art that the disclosed structures and techniques could be appliedto other spectrums of image light.

First waveguide 310 includes an input grating 313 configured to incouplea first spectrum (e.g. blue image light) of image light 303 and anoutput grating 315 configured to direct the first spectrum propagatingin waveguide 310 to the eyebox area 399. Waveguide 310 may rely on TotalInternal Reflection (TIR) to confine the first spectrum of the imagelight to the waveguide 310 until output grating 315 directs the firstspectrum of the image light to the eyebox area 399. Input grating 313and output grating 315 may be diffractive gratings that are tuned for aspecific wavelength of image light. In the illustrated embodiment ofFIG. 3, input grating 313 is configured to incouple blue image light bydiffraction (e.g. first order of diffraction) along optical path 371while passing green image light (along optical path 373) and red imagelight (along optical path 374). Input grating 313 may be designed towarddiffracting 100% of blue image light in the first order and passing 100%of both green and red light undiffracted (zeroth order of diffraction).Although input grating 313 may be designed toward passing 100% of greenimage light some green image light may be diffracted (e.g. at the firstorder of diffraction) along optical path 372, as illustrated, due to thebroad range of acceptance angle and/or broad range of wavelength. Sincethis unwanted green image light has bled into the blue waveguide 310, itis desirable to outcouple the green image light propagating alongoptical path 372 before it propagates to the output grating 315 andpotentially generates green ghost images.

Input grating 313 also possesses polarization characteristics in that itis configured to transmit a first polarization orientation (e.g.s-polarization) of image light 303 and reflect a second polarizationorientation (e.g. p-polarization) of image light 303 where the firstpolarization orientation is orthogonal to the second polarizationorientation. In the specific example illustrated in FIG. 3,s-polarization is indicated by a filled circle (electric fieldoscillating orthogonal to the plane of incidence) and p-polarization isindicated by a dash perpendicular to both s-polarization and the opticalpath (electric field oscillating in the plane of incidence).

Multilayer waveplate 317 is illustrated disposed along a boundary ofwaveguide 310 that is opposite input grating 313. In an embodiment,multilayer waveplate 317 is configured to act as a half-wave plate inreflection for the first spectrum (e.g. blue image light) of image lightdiffracted by the input grating 313 and configured to act as a full-waveplate in reflection for a second spectrum (e.g. green image light) ofthe image light 303 that is diffracted by the input grating 313. Hence,when multilayer waveplate 317 receives the first spectrum of image light303 having a first polarization orientation (e.g. s-polarization)propagating along optical path 371, multilayer waveplate 317 reflectsthe first spectrum in a second polarization orientation (e.g.p-polarization) that is orthogonal to the first polarizationorientation. When multilayer waveplate 317 receive the second spectrum(e.g. green image light) of image light 303 having a first polarizationorientation (e.g. s-polarization) propagating along optical path 372,multilayer waveplate 317 reflects the second spectrum in the firstpolarization orientation. Since input grating 313 is configured totransmit light having the first polarization orientation and the secondspectrum of image light retains the first polarization orientation afterencountering multilayer waveplate 317, the second spectrum of imagelight passes through input grating 313 and consequently is outcoupledfrom waveguide 310, as shown in FIG. 3 (optical path 372). Therefore,the green image light that bled into waveguide 310 is outcoupled priorto reaching output grating 315 and therefore green ghost images may bereduced. Meanwhile, the first spectrum of image light is reflected byinput grating 313 and continues propagating along optical path 371(confined by waveguide 310) until encountering output grating 315, whichdirects the first spectrum of image light to eyebox area 399 alongexample optical paths 381A and 381B.

In an embodiment, multilayer waveplate 317 is configured to retard thefirst spectrum of image light propagating along optical path 371 by afirst retardation value that is a half-wave (λ/2) or an integer plus ahalf-wave (e.g. 3λ/2 or 5λ/2) and multilayer waveplate 317 is furtherconfigured to retard the second spectrum of image light propagatingalong optical path 372 by a second retardation value that is multiple ofa full-wave (e.g. λ, 2λ, 3λ . . . ). Therefore, this configuration ofmultilayer waveplate 317 generates orthogonal polarization orientationin reflection for the first and second spectrums. In this configuration,the multilayer waveplate 317 may be configured to retard undiffractedgreen image light propagating along optical path 373 by a thirdretardation value that changes the polarization orientation of theundiffracted green image light. The third retardation value may be λ/2,3λ/2, or 5λ/2, for example. The multilayer waveplate 317 may also beconfigured to retard undiffracted red image light propagating alongoptical path 374 by the third retardation value that changes thepolarization orientation of the undiffracted red image light. The thirdretardation value may be λ/2, 3λ/2, or 5λ/2, for example.

Multilayer waveplate 317 may include a birefringent film designedaccording to the techniques described by G. D. Sharp and J. R. Birge in“Retarder Stack Technology for Color Manipulation,” SID, 1999. In thesedesigns, the thin films included in the multilayer waveplates retardlight on a color-selective basis to achieve the desired polarizationorientation for specific colors of light. The film material and thethickness of the film materials are manipulated to achieve the desiredresults with respect to color selectivity and polarization orientation.A birefringent film may be fabricated by liquid crystal polymer orstretching polymer, for example. The other multilayer waveplatesdescribed in this disclosure may be designed using the techniquesdescribed by Sharp and Birge to achieve the configurations disclosedherein.

FIG. 4 illustrates example configurations of the multilayer waveplatesillustrated in FIG. 3, in accordance with an embodiment of thedisclosure. FIG. 4 illustrates that example multilayer waveplate 317 isconfigured to act as a half-wave plate in transmission for a thirdspectrum (e.g. red image light) of image light 303 that is notdiffracted by input grating 313 (optical path 374). Example multilayerwaveplate 317 is also configured to act as a half-wave plate intransmission for the second spectrum (e.g. green image light) of imagelight 303 that is not diffracted by input grating 313 (optical path373). Since multilayer waveplate 317 acts as a half-wave plate for lightpropagating along optical paths 373 and 374, the polarizationorientation for light propagating along optical paths 373 and 374 isconverted from the first polarization orientation (e.g. s-polarization)to the second polarization orientation (e.g. p-polarization), asindicated in FIG. 4. Light that is passed (not diffracted) by the inputgrating 313 may transmit through multilayer waveplate 317 because theangle of incidence does not lend itself to TIR, while light diffracted(e.g. at the first order of diffraction) by input grating 313 isreflected by multilayer waveplate 317 because of the more obtuse angleof incidence, according to the principles of TIR.

FIG. 4 also shows that multilayer waveplate 317 receives the secondspectrum of image light 303 propagating along optical path 372 in thefirst polarization orientation (e.g. s-polarization) and that the secondspectrum of image light 303 propagating along optical path 372 exitsmultilayer waveplate 317 retaining the first polarization orientationsince the multilayer waveplate 317 acts a full-wave plate in reflection(half-wave coming in and half-wave in exiting) for the second spectrumpropagating along optical path 372. In one embodiment, light propagatingalong optical path 372 was diffracted by the input grating 313 at afirst order of diffraction.

For the first spectrum, multilayer waveplate 317 receives the firstspectrum of image light 303 propagating along optical path 371 in thefirst polarization orientation (e.g. s-polarization) and the firstspectrum of image light propagating along optical path 371 exitingmultilayer waveplate 317 has been converted to the second polarizationorientation (p-polarization in FIG. 4) by virtue of the half-wave platein reflection characteristics (quarter-wave coming in and quarter-wavein exiting multilayer waveplate 317) of multilayer waveplate 317. In oneembodiment, light propagating along optical path 371 was diffracted bythe input grating 313 at a first order of diffraction.

Returning to FIG. 3, second waveguide 320 includes an input grating 323configured to incouple a second spectrum (e.g. green image light) ofimage light 303 and an output grating 325 is configured to direct thesecond spectrum propagating in waveguide 320 to the eyebox area 399.Waveguide 320 may rely on TIR to confine the second spectrum of theimage light to the waveguide 320 until output grating 325 directs thesecond spectrum of the image light to the eyebox area 399. Input grating323 and output grating 325 may be diffractive gratings that are tunedfor a specific wavelength of image light in the second spectrum. In theillustrated embodiment of FIG. 3, input grating 323 is configured todiffract green image light along optical path 373 while transmitting redimage light along optical path 374. Input grating 323 may be designedtoward diffracting 100% of green image light (e.g. at first order ofdiffraction) and passing 100% of red image light (e.g. zeroth order ofdiffraction). The second spectrum of the image light is received by thesecond input grating 323 from the multilayer waveplate 317, in theillustrated embodiment. In FIG. 3, the second input grating 323 isconfigured to transmit the second polarization orientation (e.g.p-polarization) and reflect the first polarization orientation (e.g.s-polarization). Second multilayer waveplate 327 is illustrated as beingdisposed along a boundary of the second waveguide 320 that is oppositesecond input grating 323. Second multilayer waveplate 327 may beconfigured to act as a half-wave plate in reflection for the secondspectrum of image light propagating along optical path 373 so thatsecond spectrum of image light received having the second polarizationorientation received by multilayer waveplate 327 is reflected back tothe second input grating 323 in the first polarization orientation.Since the second input grating 323 is configured to reflect the firstpolarization orientation, the second spectrum of image light isreflected back into waveguide 320 by second input grating 323, asillustrated in FIG. 3. This allows the second spectrum of image light303 to continue propagating along optical path 373 (confined bywaveguide 320) until encountering output grating 325, which directs thesecond spectrum of image light to eyebox area 399 along example opticalpaths 383A and 383B.

FIG. 4 shows that multilayer waveplate 327 is also configured to act asa half-wave plate in transmission for the third spectrum (e.g. red imagelight) of image light 303 passed by the second input grating 323(optical path 374). FIG. 4 further illustrates the second spectrum ofimage light 303 being diffracted by second input grating 323(propagating along optical path 373) changing its polarizationorientation when it is reflected by the multilayer waveplate 327.

Returning again to FIG. 3, third waveguide 330 includes an input grating333 configured to incouple a third spectrum (e.g. red image light) ofimage light 303 and an output grating 335 is configured to direct thethird spectrum propagating in waveguide 330 to the eyebox area 399.Waveguide 330 may rely on TIR to confine the third spectrum of the imagelight to the waveguide 330 until output grating 335 directs the thirdspectrum of the image light to the eyebox area 399. Input grating 333and output grating 335 may be diffractive gratings that are tuned for aspecific wavelength of image light in the third spectrum. In theillustrated embodiment of FIG. 3, input grating 333 is configured toincouple the red image light by diffracting the red image light (e.g. atfirst order of diffraction) along optical path 374. Input grating 333may be designed toward diffracting 100% of red image light. The thirdspectrum of the image light 303 is received from the second multilayerwaveplate 327 in the illustrated embodiment. Third input grating 333 isconfigured to transmit the first polarization orientation and reflectthe second polarization orientation, in FIG. 3.

The third multilayer waveplate 337 in FIG. 3 is illustrated as beingdisposed along a boundary of the third waveguide 330 that is oppositethird input grating 333. Third multilayer waveplate 337 is configured toact as a half-wave plate in reflection for the third spectrum of imagelight 303. The third multilayer waveplate 337 reflects the thirdspectrum (propagating along optical path 374) back to the third inputgrating 333 in the second polarization orientation, in FIGS. 3 and 4.This allows the third spectrum of image light 303 to continuepropagating along optical path 374 (confined by waveguide 330) untilencountering output grating 335, which directs the third spectrum ofimage light to eyebox area 399 along example optical paths 384A and384B. The first, second, and third spectrums of image light 303propagating along optical paths 381A, 381B, 383A, 383B, 384A, and 384Bmay combine to form an image for viewing by a viewer of an HMD such asHMD 100.

FIG. 5 illustrates example waveguides that include a multilayerwaveplate, in accordance with an embodiment of the disclosure. Thestacked waveguide 500 of FIG. 5 is configured differently than thestacked waveguide 300 of FIG. 3 in that at least multilayer waveplate517 is configured differently than multilayer waveplate 317, inputgrating 523 is configured differently than input grating 323, andmultilayer waveplate 527 is configured differently than multilayerwaveplate 327.

Multilayer waveplate 517 is configured to act as a full-wave plate intransmission of the third spectrum (e.g. red image light) that is passedby input grating 513, whereas multilayer waveplate 317 is configured toact as a half-wave plate. As illustrated in FIG. 5, the third spectrumof image light 503 propagating along optical path 574 retains its firstpolarization orientation (e.g. s-polarization) after it is transmittedthrough multilayer waveplate 517, whereas the third spectrum of imagelight 303 propagating along optical path 374 changes polarizationorientation after propagating through multilayer waveplate 317. FIG. 6also indicates the full-wave plate configuration of multilayer waveplate517 with respect to optical path 574.

Multilayer waveplate 517 is also configured to act as a full-wave platein transmission of the second spectrum (e.g. green image light) that ispassed by input grating 513, whereas multilayer waveplate 317 isconfigured to act as a half-wave plate. As illustrated in FIG. 5, thesecond spectrum of image light 503 propagating along optical path 573retains its first polarization orientation (e.g. s-polarization) afterit is transmitted through multilayer waveplate 517, whereas the secondspectrum of image light 303 propagating along optical path 373 changespolarization orientation after propagating through multilayer waveplate317. FIG. 6 also indicates the full-wave plate configuration ofmultilayer waveplate 517 with respect to optical path 573.

Second input grating 523 is configured to transmit the firstpolarization orientation (e.g. s-polarization) and reflect the secondpolarization orientation (e.g. p-polarization), whereas second inputgrating 323 is configured to transmit the second polarizationorientation and reflect the first polarization orientation.

Second multilayer waveplate 527 is configured to act as a full-waveplate in transmission of the third spectrum (e.g. red image light)passed by second input grating 523, whereas multilayer waveplate 327 isconfigured to act as a half-wave plate. As illustrated in FIG. 5, thethird spectrum of image light 503 propagating along optical path 574retains its polarization orientation after it is transmitted throughmultilayer waveplate 527. FIG. 6 also indicates the full-wave plateconfiguration of multilayer waveplate 527 with respect to optical path574.

In addition to multilayer waveplate 517, input grating 523, andmultilayer waveplate 527, FIG. 5 also includes components that may beconfigured similarly to components of stacked waveguide 300 of FIG. 3.

Waveguides 510, 520, and 530, may be included in a stacked waveguide500, as illustrated. Stacked waveguide 500 includes an input portion 593and an output portion 594. The waveguides illustrated in FIG. 5 includea multilayer waveplate that also act to reduce optical crosstalk byoutcoupling unwanted image light from the waveguides before the unwantedimage light is directed to the eyebox area 399 by a given output grating(e.g. 515, 525, or 535).

FIG. 5 includes a first waveguide 510, a second waveguide 520, and athird waveguide 530. First waveguide 510 is configured to incouple afirst spectrum of image light 503 into the waveguide 510 and direct thefirst spectrum into the eyebox area 399. In one embodiment, the firstspectrum of image light is blue light. The blue light may be within arange of between 450 and 480 nm, in some embodiments. Second waveguide520 is configured to incouple a second spectrum of image light 503 intothe waveguide 520 and direct the second spectrum into the eyebox area399. In one embodiment, the second spectrum of image light is greenlight. The green image light may be within a range of between 500 and550 nm, in some embodiments. Third waveguide 530 is configured toincouple a third spectrum of image light 503 into the waveguide 530 anddirect the third spectrum into the eyebox area 399. In one embodiment,the third spectrum of image light is red light. The red image light maybe within a range of between 620 and 650 nm, in some embodiments.Although the waveguides 510, 520, and 530 may be described with respectto red, green, and blue image light, it is understood by those skilledin the art that the disclosed structures and techniques could be appliedto other spectrums of image light.

First waveguide 510 includes an input grating 513 configured to incouplea first spectrum (e.g. blue image light) of image light 503 and anoutput grating 515 is configured to direct the first spectrumpropagating in waveguide 510 to the eyebox area 399. Waveguide 510 mayrely on Total Internal Reflection (TIR) to confine the first spectrum ofthe image light to the waveguide 510 until output grating 515 directsthe first spectrum of the image light to the eyebox area 399. Inputgrating 513 and output grating 515 may be diffractive gratings that aretuned for a specific wavelength of image light. In the illustratedembodiment of FIG. 5, input grating 513 is configured to incouple theblue image light by diffracting (e.g. first order diffraction) alongoptical path 571 while passing green image light (along optical path573) and passing red image light (along optical path 574). Input grating513 may be designed toward diffracting 100% of blue image light at afirst order of diffraction and passing (zeroth order of diffraction)100% of both green and red light. Input grating 513 also possessespolarization characteristics in that it is configured to transmit afirst polarization orientation (e.g. s-polarization) of image light 503and reflect a second polarization orientation (e.g. p-polarization) ofimage light 503 where the first polarization orientation is orthogonalof the second polarization orientation. In the specific exampleillustrated in FIG. 5, s-polarization is indicated by a filled circleand p-polarization is indicated by a dash perpendicular to both thes-polarization and the optical path.

Multilayer waveplate 517 is illustrated disposed along a boundary ofwaveguide 510 that is opposite input grating 513. Multilayer waveplate517 is configured to act as a half-wave plate in reflection for thefirst spectrum (e.g. blue image light) of image light propagatingoptical path 571 and configured to act as a full-wave plate inreflection for a second spectrum (e.g. green image light) of the imagelight 503 propagating along optical path 572. Hence, when multilayerwaveplate 517 receives the first spectrum of image light 503 having afirst polarization orientation (e.g. s-polarization) propagating alongoptical path 571, multilayer waveplate 517 reflects the first spectrumin a second polarization orientation (e.g. p-polarization) that isorthogonal to the first polarization orientation. When multilayerwaveplate 517 receive the second spectrum (e.g. green image light) ofimage light 503 having a first polarization orientation (e.g.s-polarization) propagating along optical path 572, multilayer waveplate517 reflects the second spectrum in the first polarization orientation,as illustrated in FIG. 5. Since input grating 513 is configured totransmit light having the first polarization orientation and the secondspectrum of image light retains the first polarization orientation afterencountering multilayer waveplate 517, the second spectrum of imagelight passes through input grating 513 and consequently is outcoupledfrom waveguide 510, as shown in FIG. 5 (optical path 572). However, thefirst spectrum of image light is reflected by input grating 513 andcontinues propagating along optical path 571 (confined by waveguide 510)until encountering output grating 515, which directs the first spectrumof image light to eyebox area 399 along example optical paths 581A and581B.

In an embodiment, multilayer waveplate 517 is configured to retard thefirst spectrum of image light propagating along optical path 571 by afirst retardation value that is a half-wave (λ/2) or an integer plus ahalf-wave (e.g. 3λ/2 or 5λ/2) and multilayer waveplate 517 is furtherconfigured to retard the second spectrum of image light propagatingalong optical path 372 by a second retardation value that is multiple ofa full-wave (e.g. λ, 2λ, 3λ . . . ). Therefore, this configuration ofmultilayer waveplate 517 generates orthogonal polarization orientationin reflection for the first and second spectrums. In this configuration,the multilayer waveplate 517 may be configured to retard undiffractedgreen image light propagating along optical path 573 by a thirdretardation value that retains the polarization orientation of theundiffracted green image light. The third retardation value may be λ,2λ, 3λ, for example. The multilayer waveplate 517 may also be configuredto retard undiffracted red image light propagating along optical path574 by the third retardation value that retains the polarizationorientation of the undiffracted red image light. The third retardationvalue may be λ, 2λ, 3λ, for example.

In embodiments, multilayer waveplate 517 may have different thicknessesto facilitate different retardation values for different optical paths.In an embodiment, multilayer waveplate 517 has a first thickness wherethe multilayer waveplate 517 receives the incoupled green image lightdiffracted by the input grating 513 and multilayer waveplate 517 has asecond thickness where the multilayer waveplate receives theundiffracted green image light (optical path 573). The second thicknessmay be greater than the first thickness to provide a sufficiently largeretardation value (e.g. λ, 2λ, 3λ) to the undiffracted green image lighttransmitted through the multilayer waveplate 517.

FIG. 6 illustrates example configurations of the multilayer waveplatesillustrated in FIG. 5, in accordance with an embodiment of thedisclosure. FIG. 6 illustrates that example multilayer waveplate 517 isconfigured to act as a full-wave plate in transmission for a thirdspectrum (e.g. red image light) of image light 503 passed by the inputgrating 513 without diffraction (optical path 574). Example multilayerwaveplate 517 is also configured to act as a full-wave plate intransmission for the second spectrum (e.g. green image light) of imagelight 503 passed by the input grating 513 without diffraction (opticalpath 573). Since multilayer waveplate 517 acts as a full-wave plate forlight propagating along optical paths 573 and 574, the polarizationorientation for light propagating along optical paths 573 and 574 isretained after passing through multilayer waveplate 517, as indicated inFIG. 6.

FIG. 6 also shows that multilayer waveplate 517 receives the secondspectrum of image light 503 propagating along optical path 572 in thefirst polarization orientation (e.g. s-polarization) and that the secondspectrum of image light 503 propagating along optical path 572 exitsmultilayer waveplate 517 retaining the first polarization orientationsince the multilayer waveplate 517 acts a full-wave plate in reflection(half-wave coming in and half-wave in exiting) for the second spectrumpropagating along optical path 572. In one embodiment, light propagatingalong optical path 572 was diffracted by the input grating 513 at afirst order of diffraction.

For the first spectrum, multilayer waveplate 517 receives the firstspectrum of image light 503 propagating along optical path 571 in thefirst polarization orientation (e.g. s-polarization) and the firstspectrum of image light propagating along optical path 571 exitingmultilayer waveplate 517 has been converted to the second polarizationorientation (p-polarization in FIG. 6) by virtue of the half-wave platein reflection (quarter-wave coming in and quarter-wave in exitingmultilayer waveplate 517) characteristic of multilayer waveplate 517. Inone embodiment, light propagating along optical path 571 was diffractedby the input grating 513 at a first order of diffraction.

Returning to FIG. 5, second waveguide 520 includes an input grating 523configured to incouple a second spectrum (e.g. green image light) ofimage light 503 and an output grating 525 is configured to direct thesecond spectrum propagating in waveguide 520 to the eyebox area 399.Waveguide 520 may rely on TIR to confine the second spectrum of theimage light to the waveguide 520 until output grating 525 directs thesecond spectrum of the image light to the eyebox area 399. Input grating523 and output grating 525 may be diffractive gratings that are tunedfor a specific wavelength of image light in the second spectrum. In theillustrated embodiment of FIG. 5, input grating 523 is configured todiffract green image (e.g. first order of diffraction) along opticalpath 573 while passing the red image light without diffraction (alongoptical path 574). Input grating 523 may be designed toward diffracting100% of green image light (e.g. at a first order of diffraction) andpassing 100% of red image light without diffraction. The second spectrumof the image light is received by the second input grating 523 throughthe multilayer waveplate 517, in the illustrated embodiment. In FIG. 5,the second input grating 523 is configured to transmit the firstpolarization orientation (e.g. s-polarization) and reflect the secondpolarization orientation (e.g. p-polarization). Second multilayerwaveplate 527 is illustrated as being disposed along a boundary of thesecond waveguide 520 that is opposite second input grating 523. Secondmultilayer waveplate 527 may be configured to act as a half-wave platein reflection for the second spectrum of image light propagating alongoptical path 573 so that second spectrum image light received having thefirst polarization orientation received by multilayer waveplate 527 isreflected back to the second input grating 523 in the secondpolarization orientation. Since the second input grating 523 isconfigured to reflect the second polarization orientation, the secondspectrum of image light is reflected back into waveguide 520 by secondinput grating 523, as illustrated in FIG. 5. This allows the secondspectrum of image light 503 to continue propagating along optical path573 (confined by waveguide 520) until encountering output grating 525,which directs the second spectrum of image light to eyebox area 399along example optical paths 583A and 583B.

FIG. 6 shows that multilayer waveplate 527 is also configured to act asa full-wave plate in transmission for the third spectrum (e.g. red imagelight) of image light 503 passed by second input grating 523 withoutdiffraction (optical path 574). FIG. 6 further illustrates the secondspectrum of image light 503 being diffracted by second input grating 523(propagating along optical path 573) changing its polarizationorientation when it is reflected by the multilayer waveplate 527.

Returning again to FIG. 5, third waveguide 530 includes an input grating533 configured to incouple a third spectrum (e.g. red image light) ofimage light 503 and an output grating 535 is configured to direct thethird spectrum propagating in waveguide 530 to the eyebox area 399.Waveguide 530 may rely on TIR to confine the third spectrum of the imagelight to the waveguide 530 until output grating 535 directs the thirdspectrum of the image light to the eyebox area 399. Input grating 533and output grating 535 may be diffractive gratings that are tuned for aspecific wavelength of image light in the third spectrum. In theillustrated embodiment of FIG. 5, input grating 533 is configured toincouple the red image light into waveguide 530 by diffracting the redimage light along optical path 574. Input grating 533 may be designedtoward diffracting 100% of red image light at a first order ofdiffraction. The third spectrum of the image light 503 is receivedthrough the second multilayer waveplate 527 in the illustratedembodiment. Third input grating 533 is configured to transmit the firstpolarization orientation and reflect the second polarizationorientation, in FIG. 5.

The third multilayer waveplate 537 in FIG. 5 is illustrated as beingdisposed along a boundary of the third waveguide 530 that is oppositethird input grating 533. Third multilayer waveplate 537 is configured toact as a half-wave plate in reflection for the third spectrum of imagelight 503. The third multilayer waveplate 537 reflects the thirdspectrum (propagating along optical path 574) back to the third inputgrating 533 in the second polarization orientation, in FIGS. 5 and 6.This allows the third spectrum of image light 503 to continuepropagating along optical path 574 (confined by waveguide 530) untilencountering output grating 535, which directs the third spectrum ofimage light to eyebox area 399 along example optical paths 584A and584B. The first, second, and third spectrums of image light 503propagating along optical paths 581A, 581B, 583A, 583B, 584A, and 584Bmay combine to form an image for viewing by a viewer of an HMD such asHMD 100, for example.

In an embodiment of stacked waveguide 500, multilayer waveplate 517 isincluded in stacked waveguide 500 while multilayer waveplates 527 and/or537 are/is not included and instead TIR is relied upon to confine theincoupled image light to the waveguides 520 and/or 530, respectively.Green image light bleeding into waveguide 510 may be the largest causeof ghost images while unwanted spectrums of image light bleeding intowaveguides 520 and 530 may be of lesser concern. For the same reasons,stacked waveguide 300 may include multilayer waveplate 317 but notmultilayer waveplate 327 and/or 337.

Embodiments of the invention may include or be implemented inconjunction with an artificial reality system. Artificial reality is aform of reality that has been adjusted in some manner beforepresentation to a user, which may include, e.g., a virtual reality (VR),an augmented reality (AR), a mixed reality (MR), a hybrid reality, orsome combination and/or derivatives thereof. Artificial reality contentmay include completely generated content or generated content combinedwith captured (e.g., real-world) content. The artificial reality contentmay include video, audio, haptic feedback, or some combination thereof,and any of which may be presented in a single channel or in multiplechannels (such as stereo video that produces a three-dimensional effectto the viewer). Additionally, in some embodiments, artificial realitymay also be associated with applications, products, accessories,services, or some combination thereof, that are used to, e.g., createcontent in an artificial reality and/or are otherwise used in (e.g.,perform activities in) an artificial reality. The artificial realitysystem that provides the artificial reality content may be implementedon various platforms, including a head-mounted display (HMD) connectedto a host computer system, a standalone HMD, a mobile device orcomputing system, or any other hardware platform capable of providingartificial reality content to one or more viewers.

The term “processing logic” in this disclosure may include one or moreprocessors, microprocessors, multi-core processors, Application-specificintegrated circuits (ASIC), and/or Field Programmable Gate Arrays(FPGAs) to execute operations disclosed herein. In some embodiments,memories (not illustrated) are integrated into the processing logic tostore instructions to execute operations and/or store data. Processinglogic may also include analog or digital circuitry to perform theoperations in accordance with embodiments of the disclosure.

A “memory” or “memories” described in this disclosure may include one ormore volatile or non-volatile memory architectures. The “memory” or“memories” may be removable and non-removable media implemented in anymethod or technology for storage of information such ascomputer-readable instructions, data structures, program modules, orother data. Example memory technologies may include RAM, ROM, EEPROM,flash memory, CD-ROM, digital versatile disks (DVD), high-definitionmultimedia/data storage disks, or other optical storage, magneticcassettes, magnetic tape, magnetic disk storage or other magneticstorage devices, or any other non-transmission medium that can be usedto store information for access by a computing device.

Communication channels may include or be routed through one or morewired or wireless communication utilizing IEEE 802.11 protocols,BlueTooth, SPI (Serial Peripheral Interface), I²C (Inter-IntegratedCircuit), USB (Universal Serial Port), CAN (Controller Area Network),cellular data protocols (e.g. 3G, 4G, LTE, 5G), optical communicationnetworks, Internet Service Providers (ISPs), a peer-to-peer network, aLocal Area Network (LAN), a Wide Area Network (WAN), a public network(e.g. “the Internet”), a private network, a satellite network, orotherwise.

The above description of illustrated embodiments of the invention,including what is described in the Abstract, is not intended to beexhaustive or to limit the invention to the precise forms disclosed.While specific embodiments of, and examples for, the invention aredescribed herein for illustrative purposes, various modifications arepossible within the scope of the invention, as those skilled in therelevant art will recognize.

These modifications can be made to the invention in light of the abovedetailed description. The terms used in the following claims should notbe construed to limit the invention to the specific embodimentsdisclosed in the specification. Rather, the scope of the invention is tobe determined entirely by the following claims, which are to beconstrued in accordance with established doctrines of claiminterpretation.

What is claimed is:
 1. An optical structure comprising: an input gratingconfigured to incouple a first spectrum of received image light, whereinthe input grating is configured to transmit a first polarizationorientation of the image light and reflect a second polarizationorientation of the image light; and a multilayer waveplate configured toreflect the first spectrum of the image light incoupled by the inputgrating in the second polarization orientation and reflect a secondspectrum of the image light incoupled by the input grating bydiffraction in the first polarization orientation.
 2. The opticalstructure of claim 1, wherein the multilayer waveplate is configured toact as a half-wave plate in reflection for the first spectrum of theimage light diffracted by the input grating and configured to act as afull-wave plate in reflection for the second spectrum of the image lightdiffracted by the input grating.
 3. The optical structure of claim 2,wherein the multilayer waveplate is configured to act as a half-waveplate in transmission for a third spectrum of the image light that isundiffracted by the input grating, and wherein the multilayer waveplateis configured to act as a half-wave plate in transmission for the secondspectrum of the image light that is undiffracted by the input grating.4. The optical structure of claim 3 further comprising: a second inputgrating configured to incouple the second spectrum of the image light,the second spectrum of the image light received through the multilayerwaveplate, wherein the second input grating is configured to transmitthe second polarization orientation and reflect the first polarizationorientation; and a second multilayer waveplate configured to act as ahalf-wave plate in reflection for the second spectrum of the image lightdiffracted by the second input grating, the second multilayer waveplatereflecting the second spectrum of the image light back to the secondinput grating in the first polarization orientation.
 5. The opticalstructure of claim 4 further comprising: a third input gratingconfigured to incouple the third spectrum of the image light, the thirdspectrum of the image light received from the second multilayerwaveplate, wherein the third input grating is configured to transmit thefirst polarization orientation and reflect the second polarizationorientation; and a third multilayer waveplate configured to act as ahalf-wave plate in reflection for the third spectrum of the image lightdiffracted by the third input grating, the third multilayer waveplatereflecting the third spectrum of image light back to the third inputgrating in the second polarization orientation.
 6. The optical structureof claim 2, wherein the multilayer waveplate is configured to act as afull-wave plate in transmission for a third spectrum of the image lightthat is undiffracted by the input grating, and wherein the multilayerwaveplate is configured to act as a full-wave plate in transmission forthe second spectrum of the image light that is undiffracted by the inputgrating.
 7. The optical structure of claim 6 further comprising: asecond input grating configured to incouple the second spectrum of theimage light, the second spectrum of the image light received through themultilayer waveplate, wherein the second input grating is configured totransmit the first polarization orientation and reflect the secondpolarization orientation; and a second multilayer waveplate configuredto act as a half-wave plate in reflection for the second spectrum of theimage light diffracted by the second input grating, the secondmultilayer waveplate reflecting the second spectrum of image light backto the second input grating in the second polarization orientation. 8.The optical structure of claim 7 further comprising: a third inputgrating configured to incouple the third spectrum of the image light,the third spectrum of the image light received through the secondmultilayer waveplate, wherein the third input grating is configured totransmit the first polarization orientation and reflect the secondpolarization orientation; and a third multilayer waveplate configured toact as a half-wave plate in reflection for the third spectrum of theimage light diffracted by the third input grating, the third multilayerwaveplate reflecting the third spectrum of image light back to the thirdinput grating in the second polarization orientation.
 9. The opticalstructure of claim 1, wherein the first spectrum includes blue light,and wherein the second spectrum includes green light.
 10. The opticalstructure of claim 1 further comprising: an output grating, wherein theoutput grating is configured to receive the first spectrum of the imagelight and direct the first spectrum of the image light as a portion ofan image.
 11. A waveguide comprising: a blue input grating configured toincouple blue image light into the waveguide, wherein the blue inputgrating is configured to transmit a first polarization orientation ofthe image light and reflect a second polarization orientation of theimage light; a multilayer waveplate configured to reflect the blue imagelight incoupled by the blue input grating in the second polarizationorientation and reflect green image light incoupled by the blue inputgrating in the first polarization orientation; and an output gratingconfigured to direct the blue image light to an eyebox area.
 12. Thewaveguide of claim 11, wherein the multilayer waveplate is configured toretard the blue image light by a first retardation value in reflectionand configured to retard the green image light diffracted by the blueinput grating by a second retardation value in reflection, wherein thesecond retardation value is a multiple of a full-wave and the firstretardation value is a half-wave or an integer plus a half-wave.
 13. Thewaveguide of claim 12, wherein the multilayer waveplate is configured toretard undiffracted green image light at a third retardation value intransmission, the undiffracted green image light passing through theblue input grating undiffracted, the third retardation value changing apolarization orientation of the undiffracted green image light.
 14. Thewaveguide of claim 12, wherein the multilayer waveplate is configured toretard undiffracted green image light at a third retardation value intransmission, the undiffracted green image light passing through theblue input grating undiffracted, the third retardation value retaining apolarization orientation of the undiffracted green image light.
 15. Thewaveguide of claim 14, wherein the multilayer waveplate has a firstthickness where the multilayer waveplate receives the incoupled greenimage light diffracted by the blue input grating, and wherein themultilayer waveplate has a second thickness where the multilayerwaveplate receives the undiffracted green image light, the secondthickness being greater than the first thickness.
 16. The waveguide ofclaim 11, wherein the multilayer waveplate includes a birefringent film.17. A Head Mounted Display (HMD) comprising: a display for providingimage light; and an optical structure to receive the image light anddirect the image light in an eyebox direction, the optical structurecomprising: an input grating configured to incouple a first spectrum ofreceived image light, wherein the input grating is configured totransmit a first polarization orientation of the image light and reflecta second polarization orientation of the image light; and a multilayerwaveplate configured to reflect the first spectrum of the image lightincoupled by the input grating in the second polarization orientationand reflect a second spectrum of the image light incoupled by the inputgrating by diffraction in the first polarization orientation.
 18. TheHMD of claim 17, wherein the multilayer waveplate is configured to actas a half-wave plate in reflection for the first spectrum of the imagelight diffracted by the input grating and configured to act as afull-wave plate in reflection for the second spectrum of the image lightdiffracted by the input grating.
 19. The HMD of claim 18, wherein themultilayer waveplate is configured to act as a half-wave plate intransmission for a third spectrum of the image light that isundiffracted by the input grating, and wherein the multilayer waveplateis configured to act as a half-wave plate in transmission for the secondspectrum of the image light that is undiffracted by the input grating.20. The HMD of claim 17, wherein the multilayer waveplate includes abirefringent film.